Manyang told lawmakers in Western Equatoria state, where violence has flared in recent weeks, that Machar's armed opposition group was responsible for a string of killings in Mundri West County in recent weeks, including that of the county's executive director, John Kaloipa.

Manyang said a group of armed youths, known as "Arrow Boys," attacked an SPLA base near the border with the Democratic Republic of Congo last week, killing one army soldier and wounding three others.

A spokesman for Machar's rebel group, James Gatdet Dak, confirmed that the armed opposition movement, known as the SPLM-in-Opposition (SPLM-IO), is in Western Equatoria state and has been actively recruiting fighters, including youths who have joined the Arrow Boys. But Manyang denied that the opposition fighters were responsible for the spate of killings in the state.

"The state government has confirmed that it is the government forces killing civilians, not our forces," Gatdet said. South Sudan in Focus was not able to confirm that Western Equatoria officials have made any such statement.

Gatdet said a former director of research at South Sudan's ministry of defense, Major Lasuba Lodoru Wongo, who set up a new rebel group in Western Equatoria state in January, has aligned himself with the the SPLM-IO.

"He is one of our senior officers on the ground there," Manyang said.

Mundri West County is around 250 miles northwest of the national capital, Juba.

Manyang says more government forces have been sent to Mundri West following the recent clashes there.

The spread of the fighting to Western Equatoria state, and the recent escalation of violence in the two oil-producing states of Unity and Upper Nile, comes days before talks to end the 18-month-old conflict in South Sudan are due to resume in Addis Ababa.